1. Field
Aspects of the present invention generally relate to rotary knob friction adjustment control and more specifically relates to controlling rotational positions of knobs in a trip unit of a circuit breaker by friction, force, and/or pressure.
2. Description of the Related Art
Use of rotary knobs to provide a mechanical control of some parameter is well known. This control is enabled by providing finite rotational positions of the knobs. The rotational positions can be controlled by friction, force, and/or pressure. For example, control of rotational positions of knobs may be needed in a trip unit of a circuit breaker.
In the past the trip unit housings have been usually designed as two halves (two structural parts) split right through the centre of rotation of the knobs. These two halves, knobs and flat step operation springs are put together as a blind assembly. Knob control can be done with dents on the knobs. Dents may be crescent-shaped grooves being paired with corresponding plastic flexible fingers snapping in the grove for predetermined rotational knob position. All parts (knobs and housing halves) are usually hard plastic injection molded parts, but tight tolerances are necessary to make such an assembly possible. However, the tight tolerances made assemblies more expensive.
Therefore, there is a need for improvements in rotary knob friction adjustment control for applications such as in a trip unit of a circuit breaker.